Trigger With The When Condition

create table Emp_tab as select * from emp where 1=2;

Table created.

CREATE OR REPLACE TRIGGER Print_salary_changes

BEFORE

DELETE OR INSERT OR UPDATE ON Emp_tab

      FOR EACH ROW

    WHEN (new.Empno > 0)

    DECLARE

        sal_diff number;

    BEGIN

        sal_diff  := :new.sal  - :old.sal;

        dbms_output.put('Old salary: ' || :old.sal);

       dbms_output.put('  New salary: ' || :new.sal);

       dbms_output.put_line('  Difference ' || sal_diff);

 END;

insert into Emp_tab ( select * from emp where deptno=10);

Old salary:   New salary: 2450  Difference

Old salary:   New salary: 5000  Difference

Old salary:   New salary: 1300  Difference

3 rows created.

update Emp_tab set sal=9000;

Old salary: 2450  New salary: 9000  Difference 6550

Old salary: 5000  New salary: 9000  Difference 4000

Old salary: 1300  New salary: 9000  Difference 7700

3 rows updated.

delete Emp_tab;

3 rows deleted.